The present invention relates to mounting systems for sheet material, particularly thermo-expansive and contractive architectural sheet material such as polycarbonate and acrylic sheeting, and to such systems by which such sheet material is employed in building and like structures as a structural surface thereof, a skylight assembly, or the like.
Various forms of polycarbonate, acrylic and like plastic sheet material, ordinarily of a transparent or translucent form, have come into widespread use in recent years as a relatively low-cost substitute for glass. Examples of such sheeting include LEXAN brand polycarbonate plastic sheeting manufactured by General-Electric Company, Sheet Products Section, Pittsfield, Mass., similar polycarbonate sheeting manufactured by Sheffield Plastics Corp., Sheffied, Mass., and PLEXIGLAS brand methyl acrylate plastic sheeting manufactured by Rohm & Haas Company, Philadelphia, Pa. Such types of plastic sheeting are readily susceptible of virtually any use to which sheet glass is conventionally put, particularly in architectural and structural uses in the construction of buildings and like structures. Furthermore, because such types of plastic sheeting are more flexible and resilient than glass, such sheeting may be employed in curved or molded forms in which glass is either unavailable or prohibitively expensive. By way of example, such plastic sheeting is now conventionally used in windows, storm doors, skylights, greenhouses, shelters such as bus stops, and many other like embodiments.
In the conventional manner by which ordinary glass is mounted, such plastic sheeting is mounted in place by use of a supporting framework, typically aluminum framing members, which encloses and seals the edges of each individual sheet. It is known in the art that ordinary glass and conventional framing materials such as aluminum have generally comparable thermo-expansional and contractional properties and therefore no particular engineering or design problems are presented in constructing supporting framework for ordinary glass. However, in contrast, it is also known in the art that plastic sheeting of the type presently concerned is substantially more expansively and contractively sensitive to temperature changes than are ordinary glass and conventional framing materials. Accordingly, particular provisions must be made in the construction and design of supporting framework for such plastic sheeting in order to accommodate dimensional changes therein likely to occur due to expected ordinary temperature changes in the intended environment of the sheeting. Under conventional practice, conventional glass mounting framework is employed for such plastic sheeting with open spacings being provided in the supporting framework for expansion thereinto of the sheeting material. In the past, substantial problems have been encountered in mounting such plastic sheets in an acceptable manner meeting the two-fold requirements of adequately providing for expansion and contraction of the sheets while also obtaining watertight seals at the mounted edges of the sheets. To alleviate water leakage problems in mounting systems of such plastic sheeting, it has become conventional practice and wisdom that such plastic sheeting must be employed in relatively small sheets to achieve a reduced absolute amount of potential expansion and contraction per sheet and thereby presumably reduce expansionally and contractionally-related leakage problems. However, because such an approach generally requires a greater number of sheets in any particular mounting system and therefore requires a greater number of sealed sheet edges, the number of possible leakage points is significantly increased by this approach and, in practice, leakage problems persist in systems employing this approach.
At least certain brands of the plastic sheeting presently concerned, specifically LEXAN and SHEFFIELD polycarbonate sheeting, are manufactured and available in continuous lengths of up to several hundred feet or more having uniform widths of between approximately four and eight feet and marketed either in flat sheet form of relatively short lengths or in considerably greater lengths rolled for convenience onto a suitable spool. The availability of such continuous length plastic sheeting is not widely known and, in any event, is not considered to provide any particular advantages in the uses of the sheeting because of the above-discussed conventionally-recognized and understood limitations in the usable sizes of such sheeting. In fact, such continuous length sheeting is substantially only purchased by wholesale suppliers of sheeting who cut the continuous length sheeting into individual sheets of uniform conventional sizes for resale.
In contrast, the present invention provides a novel apparatus by which a continuous length of plastic or similar sheeting of virtually any length and width may be mounted so as to permit relatively free thermal expansion and contraction of the sheet while also preventing the leakage of water at the mounted edges thereof. As will be appreciated, the possible uses of the mounting apparatus are virtually limitless.